LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that are filled with inert gas and mercury. Thus, LED tube lamps are becoming an illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption; therefore, when taking into account all factors, they are typically considered a cost effective lighting option.
Typical LED tube lamps each have a variety of LED lamp components and driving circuits. The LED lamp components include LED chip-packaging elements, light diffusion elements, high efficient heat dissipating elements, light reflective boards and light diffusing boards. Heat generated by the LED lamp components and the driving elements is considerable and mainly dominates the illumination intensity such that the heat dissipation should be properly disposed to avoid rapid decrease of the luminance and the lifetime of the LED lamps. Thus, power loss, rapid light decay, and short lifetime due to poor heat dissipation tend to be factors to be considered when improving the performance of the LED illuminating system.
Nowadays, most LED tube lamps use plastic tubes and metallic elements to dissipate heat from the LEDs. The metallic elements are usually exposed to the outside of the plastic tubes. This design improves heat dissipation but heightens the risk of electric shocks. The metallic elements may be disposed inside the plastic tubes; however, the heat still remains inside the plastic tubes and deforms the plastic tubes. Deformation of the plastic tubes may also occur when the elements to dissipate heat from the LEDs are not metallic.
The metallic elements disposed to dissipate heat from the LEDs may be made of aluminum. However, aluminum is typically too soft to sufficiently support the plastic tubes when the deformation of plastic tubes occurs due to the heat as far as the metallic elements disposed inside the plastic tubes are concerned.
The conventional LED tube lamp has a tube, a circuit board with a light source deposited in the tube lamp, and two end caps on two ends of the tube lamp. A power source is installed in the end caps and electrically connected to the light source through the circuit board. An appropriate LED driver is a direct current (DC) power source, whereas the driving signal for the florescent lamp is an alternating current (AC) signal with low frequency and low voltage or an AC signal with high frequency and high voltage. The driving signals for the florescent lamp are not DC signals and have different frequencies and voltages, so they cannot be used to drive the LED without a rectification circuit.
Current ways of using LED lamps, such as LED tube lamps, to replace traditional lighting devices (referring mainly to fluorescent lamps) include using a ballast-compatible LED tube lamp. Typically, because there is no need to change the electrical or conductive wirings in the traditional lamps, an LED tube lamp can be used to directly replace (e.g., a fluorescent lamp). Common main types of ballasts include inductive (magnetic) ballast and electronic ballast, and common electronic ballasts can include instant-start ballasts and program-start ballasts. The inductive ballast only use one single coil to provide a high voltage pulses needed to start the fluorescent lamp and limit the maximum tube current. An electronic ballast typically includes a resonant circuit and is designed to match the loading characteristics of a fluorescent lamp in driving the fluorescent lamp. For example, for properly starting a fluorescent lamp, the electronic ballast provides driving methods respectively corresponding to the fluorescent lamp working as a capacitive device before emitting light, and working as a resistive device upon emitting light. But an LED is a nonlinear component with different characteristics from a fluorescent lamp. Therefore, using an LED tube lamp with an electronic ballast impacts the resonant circuit design of the electronic ballast, which may cause a compatibility problem.